1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and, more particularly, to a semiconductor integrated circuit achieving a reduction of power consumption by using a transistor having a high threshold voltage to cut the supply of power to an unused circuit.
2. Background Art
The power supply voltage of semiconductor integrated circuits has fallen year by year along with the reduction of power consumption and the miniaturization of processing dimensions. When a signal amplitude becomes small due to the reduction of the power supply voltage, the threshold voltage of a transistor becomes high relative to the signal amplitude, so an on current of the transistor decreases and a delay increases. For this reason, the threshold voltage of the transistor also must be made lower along with the power supply voltage. However, a leakage current in an off state increases when the threshold voltage of the transistor is lowered, so there is the disadvantage that reduction of the power consumption is obstructed.
As technology preventing the increase of such leakage current, the “multi-threshold complementary metal oxide semiconductor” (MTCMOS) circuit technology is known. In a MTCMOS, for example, a transistor switch having a high threshold voltage is arranged in a power line of each circuit block performing a specific function. When the circuit block becomes unused in state, the transistor switch is set to the off position and the leakage current flowing through each transistor in the circuit block is shut off. By this, useless leakage current flowing through unused circuit blocks can be greatly reduced.